The superparamagnetic effect, which occurs when magnetic grains become too tiny, is a major limitation in constructing magnetic devices, such as recording media for high density hard disk drives or Magnetic Random Access Memory (MRAM) system. One promising solution is to use patterned magnetic media, where magnetic layers comprise arrays of separated magnetic elements.
While promising, several hurdles remain in successfully implementing patterned magnetic media. First, the implementation of conventional patterned magnetic media still involves the use of undesirably-high levels of switching fields as produced by magnetic write heads due to the need to use materials with high anisotropy required for sufficient thermal stability. Particularly with respect to magnetic elements that are homogeneous, such high anisotropy translates into high reversal fields, which are hard to switch in realistic recording systems. Second, the implementation of such patterned magnetic media typically suffers from excessive amounts of adjacent element overwriting, in which the magnetic fields generated by a write head not only affect a given magnetic element but also affect one or more neighboring magnetic elements in an undesired manner.
Recently, composite media have been investigated for use as the magnetic elements in patterned media. Such composite media are formed by positioning two or more layers of different magnetic elements upon one another in a stacked manner so as to form an overall composite magnetic element. In particular, such composite media typically employ one or more magnetically soft element(s) in an alternating, stacked (layered) arrangement with one or more magnetically hard element(s). By using such alternating layers of hard and soft element(s), the overall composite magnetic elements can be influenced (in terms of their magnetization) by reversal fields that are of a significantly lower magnitude than those used with homogenous magnetic elements, while at the same time can achieve the same thermal stability and the same reliable recording levels achieved through the use of magnetic elements that are strictly hard in terms of their material properties.
Although the reversal fields that can be used to write to patterned media using composite magnetic elements are lower than those used to write to patterned media using homogenous elements, the reversal fields nevertheless still may be undesirably high. Moreover, a substantial reduction of the reversal field is achieved only for elements of a significant height, which may further increase the requirements for the head fields. In addition, as mentioned above, a significant concern in designing and implementing magnetic media is that adjacent element overwriting be avoided and that the magnetic media be capable of achieving improved writing margins. Although closely-packed magnetic elements in patterned media are desirable for increasing recording capacity, when high reversal fields are used to write to a given composite magnetic element, there is still a significant chance that neighboring magnetic elements will be affected (or reversed) by stray magnetic fields generated by the writing device.
It would therefore be advantageous if an improved form of magnetic media could be developed that was capable of operating with even lower levels of reversal fields than those employed with conventional patterned media employing composite magnetic elements, so as to allow for both high recording capacity and at the same time minimize adjacent element overwriting.